The prior art relating to this invention is described by using an example of interconnector materials of LSI.
At present, interconnector materials such as Al, Al-Si alloys containing several percent of Si, and Al-Si-Cu alloys containing a slight amount of Cu are used for LSI. As the integration density of LSI becomes higher, interconnectors are getting thinner and longer and the number of interconnectors is increasing. Furthermore, higher speed operation is also required for LSI as well as higher integration density. As a result, the density of the electric current flowing through interconnectors increases as LSI has higher integration density and higher quality.
However, high electric current causes atoms in metal to move in the opposite direction of the electric current and finally results in the disconnection of interconnectors. This phenomenon is known as electromigration, which is one of the most important factors in designing the reliability of metal interconnectors.
Therefore, a lot of efforts are put into the development of materials having higher resistance to electromigration to manufacture higher quality LSI. In order to shorten development period, testing methods which can evaluate the electromigration resistance of conductive materials in short time are required.
A prior art testing method of the electromigration resistance is explained below.
An amount of electric current used in LSI performance is usually less than 10.sup.5 A/cm.sup.2. In the test, a current of about 10.sup.6 A/cm.sup.2 is applied to interconnectors to accelerate electromigration. The test is also carried out at an ambient temperature of about 250.degree. C. to increase the deterioration rate of interconnectors.
However, it takes a long time even in such acceleration tests until the breakdown of the interconnectors takes place: for example, it takes at least one month in the case of Al-Si alloy. Therefore, the life of interconnector is estimated from the elapsed time by which the resistance of the interconnector increases 5 or 10 percent. Nevertheless, most cases still required a few weeks to one month until the resistance increase even 5%. It will take a longer time for the materials to be developed because of higher resistance to electromigration, suggesting that these conventional methods are not a practical testing method employed during the development of new interconnector materials.
It is also found from the tests using higher current density that higher current density causes the overheating of the interconnector, resulting in the rise of the resistance of interconnector which causes the interconnect to be further heated. Namely, it is impossible to maintain the temperature of the interconnector at a prescribed value. When high current density is applied, the temperature can not be controlled and the interconnector melts to disconnection, showing that the test of electromigration can not be attained.
As mentioned above, it is actually impossible to evaluate the electromigration resistance in short period. In order to overcome above-mentioned problems, this invention is to provide a testing method and apparatus for conductive materials using electric current which makes it possible to evaluate the electromigration resistance of conductive materials in short time.